Long-term outcomes of subcutaneous ICD therapy in arrhythmogenic cardiomyopathy: a multicentre cohort study

Aims The implantable cardioverter-defibrillator (ICD) is the most effective therapy for the prevention of sudden cardiac death (SCD) in patients with arrhythmogenic cardiomyopathy (ACM). However, transvenous systems are burdened by long-term complications. The subcutaneous ICD (S-ICD) represents a promising alternative, although long-term evidence in ACM remains scarce. We aimed to report the long-term outcomes of S-ICD therapy in the largest multicenter cohort of ACM patients with different phenotypic variants to date. Methods In this multicenter observational study, 123 consecutive ACM patients(mean age 40±5 years; 67% male) underwent S-ICD implantation using the intermuscular technique between June 2016 and December 2024.The phenotypic variant of ACM was “right-dominant” ACM phenotype in 31 (25%) patients, “biventricular” ACM phenotype in 57(46%) patients and “left- dominant” ACM phenotype in 35(29%) patients according to the 2024 European Task Force consensus diagnostic criteria. Seventeen percent of patients were implanted for secondary prevention (ventricular fibrillation, n = 5; sustained ventricular tachycardia, n =16). Fourteen (11%) patients had a previous transvenous ICD. Results Defibrillation testing was successful in 98.9% of patients at ≤65 J, with no peri-procedural complications. Over a median follow-up of 46 months (IQR 29–60), appropriate shocks (monomorphic ventricular tachycardia in 28, ventricular fibrillation in 11) occurred in 18 patients (15%), corresponding to an annualized rate of 3.8%(95% CI 2.3–6.0) and a 5-year cumulative incidence of 18.8% (95% CI 10.5–27.1). All first shocks were effective (100%). A “right-dominant” phenotype independently predicted appropriate shocks (HR 2.53; 95% CI 1.00–6.38). Inappropriate shocks (ISs) occurred in 15 patients (12%), with an annualized rate of 3.2% (95% CI 1.8–5.2) and a 5-year cumulative incidence of 15.8% (95% CI 8.0–23.6). The most common reason for ISs was non-cardiac oversensing (47%, 7/15), followed by paroxysmal supraventricular tachycardia(33%, 5/15) and T-wave oversensing (20%, 3/15). The source of non-cardiac oversensing was myopotentials (n=5) and external noise (n=2). All myopotential-related ISs occurred during sports activities. Device-related complications were infrequent (2%), and no device explantations were required due to pacing indications, anti-tachycardia pacing or ineffective therapy. Conclusions This large multicenter study with long-term follow-up supports the S-ICD as a safe and effective alternative to transvenous ICDs for the prevention of sudden cardiac death in patients with ACM without pacing indications. The “right-dominant” ACM phenotype emerged as a predictor of appropriate therapy, underscoring the importance of phenotypic characterization in risk stratification. The risk of inappropriate shocks—mainly related to non-cardiac oversensing—is acceptable, and the rate of device-related complications is very low.